The Onmitsukidō (隠密機動, secret tactics), also called the Secret Mobile Unit/Corps, Special Forces or Covert Ops, is the second largest organization that Shinigami join, and one of the three main branches of military in Soul Society.
Although by nature an organization separate from the Gotei 13, the clan which possessed superior abilities as Shinigami among the Four Noble Families, the Shihōin Clan, fill the role of the Commander-in-Chief throughout the generations, while also having their clan leader take the post of division captain within the Gotei 13.
The Onmitsukidō is one of the three forces under the direct supervision of the Central 46 Chambers. If the Gotei 13 operate openly, the Onmitsukidō patrols and conducts surveillance in enemy territory and carries out top-secret operations, such as assassinations and the execution of Shinigami who have broken the law. If the Gotei 13 are considered an exterior guard, then the Onmitsukidō is an interior, covert guard.